1. Technical Field
The present invention relates to a semiconductor module in which a semiconductor unit and a cooling unit are solder-bonded to each other.
2. Related Art
The following Patent Documents are known that relate to deformation of a cooling unit of a semiconductor module.
Patent Document 1 discloses a cooling unit formed from a ceiling board, a bottom board, and a cooling agent flow path section formed between the ceiling board and the flow board. A substrate on which the heat generating body is mounted is bonded to the top surface of the ceiling board via brazing. In this cooling unit, the ceiling board has a recessed portion in which is formed a bonding surface to which the substrate is bonded, and the thickness ratio of the ceiling board to the bottom board is from 1:3 to 1:10.
Patent Document 2 discloses a heat releasing device that includes an insulated substrate having a semiconductor chip, which is the heat generating body, arranged on the front surface thereof, and a heat sink that releases the heat of the semiconductor chip and is provided on the back surface of the insulated substrate with a stress reducing member containing a stress absorbing space interposed therebetween. The heat releasing device is formed by bonding together the insulated substrate, the stress reducing member, and the heat sink via brazing. In this heat releasing device, the heat sink includes a ceiling board bonded to the stress reducing member and a bottom board that is bonded to the ceiling board and forms a flow path for a cooling fluid between itself and the ceiling board. In this heat releasing device, the thickness ratio of the ceiling board to the bottom board is in a range from 1:3 to 1:5. The heat sink includes a fin provided in the flow path of the cooling fluid to connect the ceiling board and the bottom board, the fin is bonded to ceiling board and the bottom board using vacuum brazing, and the thickness of the ceiling board is 0.8 mm.
Patent Document 3 discloses a cooling unit of a power module, in which a casing including a water path for cooling water therein is formed by combining a plurality of aluminum members. This cooling unit is formed such that the thickness ratio of a ceiling board to a bottom board of the casing is from 1:5 to 1:10. A high-purity aluminum block is secured to the ceiling board in order to secure the power module, a frame-shaped protrusion or groove is formed in the ceiling board at a position surrounding the high-purity aluminum block, and the water path is divided into a plurality of parallel flow paths by a plurality of cooling fins extending in a direction orthogonal to the longitudinal direction of the insulated substrate of the power module.
Patent Document 4 discloses a semiconductor device in which a cooling device and a metal plate exposed in a semiconductor module are bonded to each other by a bonding agent. In this semiconductor device, a recessed portion is formed in the surface bonded by the bonding agent, in a region around the bond corresponding to a region around the portion bonded to the metal plate.
Patent Document 1: Japanese Patent Application Publication No. 2010-251443
Patent Document 2: Japanese Patent Application Publication No. 2010-171279
Patent Document 3: Japanese Patent Application Publication No. 2008-288495
Patent Document 4: Japanese Patent Application Publication No. 2012-142465
In Patent Document 1 and Patent Document 2, the substrate is bonded to the cooling unit by brazing. Brazing is performed at approximately 600° C., and therefore there is more warping when the normal temperature is reached after the bonding compared to a case, such as in this application, where solder that melts at a temperature from approximately 200° C. to 350° C. that is lower than the brazing temperature is used. Accordingly, Patent Document 1 and Patent Document 2 are not suitable for a semiconductor module in which a semiconductor unit and a cooling unit are bonded by soldering.
In Patent Document 3 and Patent Document 4, a frame-shaped protrusion or groove is formed in the ceiling board, and therefore there is a problem that the machining cost is increased.